1. Field of the Invention
The present invention relates to a high pressure gas operated setting tool including a guide cylinder having a stop, a fastening element guide arranged, in a setting direction, in front of the guide cylinder and displaceable against a spring-biasing force in a direction opposite to the setting direction by a predetermined maximum amount, a drive piston axially displaceable in the guide cylinder and having a head and a stem, and a return device for displacing the drive piston to its ignition ready position.
2. Description of the Prior Art
At present, for driving of nail-shaped fastening elements in a hard structural components containing, e.g., concrete, stone or steel, explosive powder charge operated setting tools are primarily used. Such a setting tool is disclosed, e.g., in European Publication EP-0 798 084. The disclosed setting tool has a housing, a guide cylinder, a drive piston displaceable in the guide cylinder, a fastening element guide arranged in front of the guide cylinder, and a resetting device which cooperates with the fastening element guide and the drive piston. The fastening element guide is displaceable, in a direction opposite to the setting direction, against a spring biasing force. Inside the guide cylinder, there is provided an elastic element which is shaped as a hollow cylinder and surrounds the stem of the drive piston. The elastic element cushions the drive piston at the end of a drive-in process.
The resetting of the drive piston to its ignition-ready initial position is effected in two stages. In the first stage, a portion of a propellant gas, which is generated upon ignition of a cartridge, is conducted through a bypass channel, which is technically very expensive to form, from the region of the cartridge chamber into a front, in the setting direction, region of the guide cylinder. There, the portion of the propellant gas is compressed by the drive piston movable with high speed in the setting direction. After the setting process is completed, these gases expand and displace the drive piston back into its initial position. Final resetting of the drive piston to its ignition-ready initial position is effected in a second stage. First, the fastening element guide is axially displaced relative to the setting tool housing. The resetting device, which cooperates with the fastening element guide, force-lockingly cooperates with the drive piston stem and displaces the drive piston to its initial position.
A serious drawback of the known setting tool consists in that the formation of the bypass channel is very complicated and is, therefore, very expensive, which adversely affects total manufacturing costs of the tool. In addition, using the drive gas for resetting the drive piston to its initial position does not always insure adequate results.
Accordingly, an object of the present invention is to provide a setting tool with a reliable resetting of the drive piston to its initial ignition-ready position and which, at the same time, has a simple construction and can be economically produced.